Hard bias design for extra high density recording

ABSTRACT

A hard bias structure for biasing a free layer in a MR element within a read head is comprised of a composite hard bias layer having a Co 78.6 Cr 5.2 Pt 16.2 /Co 65 Cr 15 Pt 20  configuration. The upper Co 65 Cr 15 Pt 20  layer has a larger Hc value and a thickness about 2 to 10 times greater than that of the Co 78.6 Cr 5.2 Pt 16.2  layer. The hard bias structure may also include a BCC underlayer such as FeCoMo which enhances the magnetic moment of the hard bias structure. Optionally, the thickness of the Co 78.6 Cr 5.2 Pt 16.2  layer is zero and the Co 65 Cr 15 Pt 20  layer is formed on the BCC underlayer. The present invention also encompasses a laminated hard bias structure. The Mrt value for the hard bias structure may be optimized by adjusting the thicknesses of the BCC underlayer and CoCrPt layers. As a result, a larger process window is realized and lower asymmetry output during a read operation is achieved.

FIELD OF THE INVENTION

The invention relates to an improved hard bias structure formed adjacentto a giant magnetoresistive (GMR) sensor in a magnetic read head and amethod for making the same. In particular, a composite hard bias layeron a body centered cubic (BCC) underlayer is disclosed that achieves ahigh coercivity while minimizing asymmetry sigma in a read operation.

BACKGROUND OF THE INVENTION

A magnetic disk drive includes circular data tracks on a rotatingmagnetic disk and read and write heads that may form a merged head on aslider that is attached to a positioning arm. During a read or writeoperation, the merged head is suspended over the magnetic disk on an airbearing surface (ABS). The sensor in a read head is a critical componentin which different magnetic states are detected by passing a sensecurrent there through and monitoring a resistance change. One form ofmagneto-resistance is a spin valve magnetoresistance (SVMR) or giantmagnetoresistance (GMR) which is based on a configuration in which twoferromagnetic layers are separated by a non-magnetic conductive layer inthe sensor stack. One of the ferromagnetic layers is a pinned layer inwhich the magnetization direction is fixed by exchange coupling with anadjacent anti-ferromagnetic (AFM) pinning layer. The secondferromagnetic layer is a free layer in which the magnetization vectorcan rotate in response to external magnetic fields. In the absence of anexternal magnetic field, the magnetization direction of the free layeris aligned perpendicular to that of the pinned layer by the influence ofabutting hard bias layers. When an external magnetic field is applied bypassing the sensor over a recording medium on the ABS plane, themagnetic moment of the free layer may rotate to a direction which isparallel to that of the pinned layer. A sense current is used to detecta resistance value which is lower when the magnetic moments of the freelayer and pinned layer are parallel.

In a CPP configuration, a sense current is passed through the sensor ina direction perpendicular to the layers in the sensor stack.Alternatively, there is a current-in-plane (CIP) configuration where thesense current passes through the sensor in a direction parallel to theplanes of the layers in the sensor stack.

Ultra-high density (over 100 Gb/in²) recording requires a highlysensitive read head in which the cross-sectional area of the sensor istypically smaller than 0.1×0.1 microns at the ABS plane. Currentrecording head applications are typically based on an abutting junctionconfiguration in which a hard bias layer is formed adjacent to each sideof a free layer in a GMR spin valve structure. As the recording densityfurther increases and track width decreases, the junction edge stabilitybecomes more important so that edge demagnification in the free layer isprevented. In other words, horizontal (longitudinal) biasing isnecessary so that a single domain magnetization state in the free layerwill be stable against all reasonable perturbations. The criticaldimensions for sensor elements become smaller with higher recordingdensity requirements and therefore the minimum longitudinal bias fieldnecessary for free layer domain stabilization increases.

A high coercivity in the in-plane direction is needed in the hard biaslayer to provide a stable longitudinal bias that maintains a singledomain state in the free layer and thereby avoids undesirable Barkhausennoise. By arranging the flux flow of the free layer to be equal to theflux flow of the hard bias film, there are no magnetic poles at theabutting junction edges and the demagnetizing field in that vicinitybecomes zero. This condition is realized when there is a sufficientin-plane remnant magnetization (Mr) which may also be expressed as Mrtsince Mr is dependent on the thickness of the hard bias layer. Mrt isthe component that provides the longitudinal bias flux to the free layerand must be high enough to assure a single magnetic domain in the freelayer but not so high as to prevent the magnetic field in the free layerfrom rotating under the influence of a reasonably sized externalmagnetic field. Moreover, a high saturation magnetization (Ms) and ahigh squareness (S) value for Mr/Ms that approaches 1 in the hard biaslayer is desired.

Referring to FIG. 1, a conventional read head 1 based on a GMRconfiguration is shown and is comprised of a substrate 2 upon which afirst shield layer 3 and a first gap layer 4 are formed. There is a GMRelement comprised of a bottom portion 5 a, a free layer 6, and a topportion 5 b formed on the first gap layer 4. Note that the GMR elementgenerally has sloped sidewalls wherein the top portion 5 b is not aswide as the bottom portion 5 a. The GMR element may be a bottom spinvalve in which an AFM pinning layer and pinned layer (not shown) are inthe bottom portion 5 a or the GMR element may be a top spin valve wherethe AFM and pinned layers are in the top portion 5 b. There is a seedlayer 7 formed on the first gap layer 4 and along the GMR element whichensures that the subsequently deposited hard bias layers 8 have a propermicrostructure. Hard bias layers 8 form an abutting junction 12 oneither side of the free layer 6. Leads 9 are provided on the hard biaslayers 8 to carry current to and from the GMR element. The distancebetween the leads 9 defines the track width TW of the read head 1. Abovethe leads 9 and GMR element are successively formed a second gap layer10 and a second shield layer 11.

The pinned layer in the GMR element is pinned in the Y direction byexchange coupling with an adjacent AFM layer that is magnetized in the Ydirection by an annealing process. The hard bias layers 8 which are madeof a material such as CoCrPt are magnetized in the X direction asdepicted by vectors 13 and influence an X directional alignment of themagnetic vector 14 in the free layer 6. When a magnetic field ofsufficient strength is applied in the Y direction from a recordingmedium by moving the read head 1 over a hard disk (not shown) in the Zdirection, then the magnetization in the free layer switches to the Ydirection. This change in magnetic state is sensed by a voltage changedue to a drop in the electrical resistance for an electrical currentthat is passed through the MR element. In a CIP spin valve, this sensecurrent I_(s) is in a direction parallel to the planes of the sensorstack.

One concern about the output from a spin valve element during a feedback (read) operation is that the asymmetry sigma should be as small aspossible in order to accurately reproduce the waveform from therecording medium. Asymmetry is determined by the variable magnetizationdirection of the free layer. Ideally, the magnetic moment 14 of the freelayer 6 is orthogonal to the magnetic moment of the pinned layer when noexternal magnetic field is present. However, the actual angle betweenthe aforementioned magnetic moments usually deviates somewhat from 90°because of other magnetic forces in the GMR element and thereby producesan asymmetric waveform in the output.

A soft magnetic film with a high saturation flux density and comprisedof FeCoMo is employed as a magnetic pole layer in U.S. PatentPublication 2002/0150790. Referring to FIG. 2, those skilled in the artwould recognize that a FeCoMo layer can be used to modify the read headin FIG. 1 by inserting a FeCoMo underlayer 15 with a high magneticmoment between the seed layer 7 and the hard bias layer 8 (FIG. 2). Theunderlayer 15 improves the biasing efficiency and serves to reduceoutput asymmetry. A further improvement in signal amplitude andasymmetry is expected if the FeCoMo layer (or moment) can be increasedwhile the total Mrt is maintained or further reduced and the coercivityis maintained. Unfortunately, the thickness of a FeCoMo underlayer andthe associated magnetic moment contribution is limited because a thickerFeCoMo film leads to a loss of coercivity (Hc) in the hard bias layer 8.Thus, a new hard bias structure is needed which allows the thickness ofa body centered cubic (BCC) underlayer such as FeCoMo to be increasedwithout lowering H_(c) in the adjacent hard bias layer. A combination ofhigh coercivity to enhance edge junction pinning efficiency and a highermoment contribution from a BCC underlayer to further reduce asymmetrysigma has not been achieved in prior art hard bias structures to ourknowledge.

In U.S. Pat. No. 6,643,107, the electrode layers on both sides of a GMRelement are extended toward the center of a bottom spin valve and arelocated above a backed (conductive) layer on a free layer. Thisstructure prevents dead zones at the edges of the free layer andimproves output characteristics including asymmetry.

An MR sensor is described in U.S. Pat. No. 6,270,588 in which the Hexangle that is the angle between the direction of the exchange couplingmagnetic bias applied to the pinned layer and the longitudinal biasdirection is more than 90° in at least a portion of the pinned layer. Asa result, improved wave shape and better wave symmetry is achieved.

An insulating hard bias layer made of cobalt ferrite or the like is usedin U.S. Pat. No. 6,512,661 to avoid shunting of current away from a MRsensor which occurs with a conductive hard bias layer. A larger fluxdecay length is also provided which leads to a higher density recordingcapability.

In U.S. Pat. No. 6,519,121, a spin valve sensor with a composite pinnedlayer to improve biasing of the free layer is described. A CoFeHfO layeris formed on an AFM layer and a CoFe layer is formed on the CoFeHfOlayer and adjacent to a spacer layer in a MR element. This configurationminimizes sense current shunting and improves the magnetoresistiveeffect.

SUMMARY OF THE INVENTION

One objective of the present invention is to provide a hard biasstructure in which the thickness of a BCC underlayer component isincreased to enhance its moment contribution while maintaining a highcoercivity (Hc) for the hard bias structure.

A further objective of the present invention is to provide a compositehard bias layer that has a high Hc value and has good lattice matchingwith a BCC underlayer formed according to the first objective.

A still further objective of the present invention is to provide amethod of making a hard bias structure that is comprised of a BCCunderlayer and one or more hard bias layers in order to provide optimumHc and Mrt values and a reduced asymmetry output.

These objectives are achieved in a first embodiment in which a GMRelement with sidewalls and a top surface is formed on a first gap layeron a substrate in a magnetic read head. The GMR element can have a topspin valve or a bottom spin valve structure that is formed along an ABSplane and is comprised of an AFM layer, a pinned layer, a free layer,and a top surface that may be on a capping layer. The pinned layer ispinned in a first direction perpendicular to the ABS plane and parallelto the top surface of the substrate by exchange coupling with themagnetized AFM layer. A seed layer with a body centered cubic (BCC)lattice structure is formed on the first gap layer adjacent to the GMRelement. A hard bias structure is formed on a seed layer along each sideof the GMR element and contacts a substantial portion of the sidewallsin the GMR element to form abutting junctions with the free layer. Inone aspect, the hard bias structure is comprised of a BCC underlayer anda composite hard bias layer that has a lower Co_(78.6)Cr_(5.2)Pt_(16.2)layer and an upper Co₆₅Cr₁₅Pt₂₀ layer. Alternatively, the hard biasstructure comprises a BCC underlayer and an overlying Co₆₅Cr₁₅Pt₂₀layer. The BCC underlayer is preferably a ferromagnetic layer made ofFeCoMo, for example, with a high magnetic moment and that has goodlattice matching with the overlying hard bias layer.

The hard bias structure is magnetized in a direction orthogonal to thatof the pinned layer and parallel to the top surface of the substrate.The hard bias structure is magnetically coupled to the free layer andprovides a longitudinal (in-plane) bias that enables a single magneticdomain within the free layer. Electrical leads are formed above the hardbias structure and contact the GMR element along its sidewalls near thetop surface of the capping layer. A second gap layer is formed on theleads and on the GMR element and a second shield layer is formed on thesecond gap layer to complete the magnetic read head.

In a second embodiment, the magnetic read head includes the same layersas in the first embodiment except that the hard bias structure islaminated such that the BCCunderlayer/Co_(78.6)Cr_(5.2)Pt_(16.2)/Co₆₅Cr₁₅Pt₂₀ configuration isrepeated a plurality of times. Alternatively, the BCCunderlayer/Co₆₅Cr₁₅Pt₂₀ configuration is repeated a plurality of times.The thickness of the individual layers may be adjusted so that the hardbias structure has optimum Hc and Mrt values and provides a stablelongitudinal bias to an adjacent free layer in the GMR element.

The present invention is also a method of forming a magnetic read headcomprised of an improved hard bias structure according to the first andsecond embodiments. A stack of GMR layers comprised of a free layer,pinned layer, an AFM layer, and a cap layer is formed on a first gaplayer on a substrate by a conventional method. Known methods are alsoemployed to pattern a photoresist mask above the cap layer in the GMRstack. An etch process is used to define a GMR element and a trackwidth. A seed layer is deposited on exposed portions of the first gaplayer adjacent to the GMR element. An important step is formation of ahard bias structure on the seed layer and along a substantial portion ofthe sidewalls on the GMR element. The hard bias structure is formed by amagnetron sputtering or ion beam deposition (IBD) method thatsequentially forms a BCC underlayer and a hard bias layer comprised ofCo₆₅Cr₁₅Pt₂₀ or a Co_(78.6)Cr_(5.2)Pt_(16.2)/Co₆₅Cr₁₅Pt₂₀ configuration.

Alternatively, the hard bias structure may be laminated in which the BCCunderlayer/Co_(78.6)Cr_(5.2)Pt_(16.2)/Co₆₅Cr₁₅Pt₂₀ configuration or theBCC underlayer/Co₆₅Cr₁₅Pt₂₀ configuration is repeated a plurality oftimes. The thicknesses of the individual layers within the hard biasstructure are adjusted to provide optimum Hc and Mrt values whileminimizing the asymmetry sigma in the output signal during a readoperation.

The hard bias structure may be magnetically aligned in a directionparallel to the top surface of the GMR element and parallel to the ABSby applying an external magnetic field during or after the depositionstep. Electrical leads are subsequently formed on the hard biasstructure by a conventional method. The photoresist layer is thenremoved by a lift-off process, for example. The second gap layer andsecond shield layer are sequentially formed on the electrical leads andGMR element by well known methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a prior art magnetic read headwith a GMR element, a seed layer formed on a gap layer and along thesidewalls of the GMR element, and a hard bias layer on the seed layer.

FIG. 2 is a cross-sectional view of a prior art magnetic read head inwhich a hard bias structure comprised of a hard bias layer and anunderlayer is formed on a seed layer and adjacent to a GMR element.

FIG. 3 is a cross-sectional view that shows an intermediate step in themethod of forming a hard bias structure in a magnetic read headaccording to a first embodiment of the present invention.

FIG. 4 is a cross-sectional view of a magnetic read head in which a hardbias structure comprised of a CoCrPt composite hard bias layer is formedon an underlayer and adjacent to a free layer in a GMR element.

FIG. 5 is a cross-sectional view that depicts an intermediate step inthe method of forming a laminated hard bias structure in a magnetic readhead according to a second embodiment of the present invention.

FIG. 6 is a cross-sectional view of a magnetic read head in which alaminated hard bias structure comprised of a CoCrPt composite hard biaslayer on a BCC underlayer is formed adjacent to a GMR element accordingto the second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an improved hard bias structure in a magneticread head that has a high coercivity and a low output asymmetry during aread operation. The hard bias structure is useful in magnetic read headsthat are based on CIP spin valves or CPP spin valves and is alsoapplicable to MTJ devices or multi-player sensor designs as appreciatedby those skilled n the art. The drawings are provided by way of exampleand are not intended to limit the scope of the invention. For example,the shape of a GMR element in the read head is not a limitation and thepresent invention is equally applicable to any configuration where ahard bias structure according to the first or second embodiment forms anabutting junction with a free layer in a GMR element. Moreover, the GMRelement may be comprised of either a top spin valve or a bottom spinvalve. The present invention is also a method of forming a magnetic readhead with a hard bias structure according to the first or secondembodiment that has high Hc and S values and sufficient in-plane fluxdensity to ensure a single magnetic domain state in an adjacent freelayer.

A first embodiment is depicted in FIGS. 3-4. Referring to FIG. 3, across-sectional view from an ABS plane is shown of a magnetic read head20 which has a substrate 21 that may be a ceramic layer, for example. Afirst shield layer 22 is formed on the substrate 21 and a first gaplayer 23 is formed on the first shield layer by a conventional method.There is a GMR element which is a stack comprised of a bottom portion24, a free layer 25, and a top portion 26 sequentially formed on thefirst gap layer 23. The GMR element typically has sloped sidewallswherein the top portion 26 has a smaller width than the bottom portion24.

The GMR element is fabricated by sequentially depositing the layerswithin the bottom portion 24, the free layer 25, and the layers withinthe top portion 26 by a sputtering technique, for example, which is wellknown in the art. A photoresist layer 27 is patterned on the top portion26 and then an etch process is used to remove regions of the GMR stackthat are not covered by the photoresist layer 27. The etch stops on thefirst gap layer 23 which may be Al₂O₃ or silicon oxide. Note that thephotoresist layer 27 typically has an undercut along both sides at itsinterface with the top portion 26 of the GMR element to facilitate asubsequent lift-off removal step.

In one embodiment that represents a bottom spin valve, the bottomportion 24 is comprised of a seed layer such as NiCr on which ananti-ferromagnetic (AFM) pinning layer, a pinned layer, and a spacerlayer which may be Cu are sequentially formed. The individual layerswithin the bottom portion 24 are not shown in order to simplify thedrawing and direct attention to the abutting junction between the freelayer 25 and the subsequently deposited hard bias structure. The AFMlayer may be a PtMn or IrMn layer that is magnetized in the y direction.The AFM layer is exchange coupled to the pinned layer that may becomprised of CoFe and which is pinned in the y direction.

Optionally, the pinned layer may have a synthetic anti-parallel (SyAP)configuration in which a coupling layer such as Ru is sandwiched betweenan AP2 pinned layer on the AFM layer and an overlying AP1 pinned layer.The AP2 layer has a magnetic moment or vector oriented in the ydirection by exchange coupling with an AFM pinning layer. The AP1 layeris adjacent to the spacer and is anti-parallel exchange coupled to theAP2 layer via the coupling layer as is understood by those skilled inthe art. Thus, the magnetic moment or vector of the AP1 pinned layer isoriented in the “−y” direction which is anti-parallel to the magneticvector of the AP2 layer. The magnetic moments of the AP2 and AP1 layerscombine to produce a net magnetic moment that is less than the magneticmoment of a single pinned layer. A small net magnetic moment results inimproved exchange coupling between the AP2 layer and the AFM layer andalso reduces interlayer coupling between the AP1 layer and the freelayer 25.

The free layer 25 may be comprised of CoFe and/or NiFe, for example, andhas a thickness of about 20 to 50 Angstroms. The magnetization of thefree layer 25 is oriented in the x direction under the influence of alongitudinal bias from the adjoining hard bias structure which ismagnetized in the x direction and will be described in a later section.In the bottom spin valve structure, the top portion 26 of the GMRelement is comprised of a cap layer such as Ta or Ru, for example.Optionally, the cap layer may be comprised of more than one layer suchas a layer of NiCr on a layer of tantalum oxide.

In an alternative embodiment that represents a top spin valve, thebottom portion 24 may be comprised of a seed layer such as NiCr and anoptional buffer layer (not shown) in which a layer of Ru is formed onthe seed layer and a copper layer is formed on the Ru layer to provide alattice match to the overlying free layer 25. The magnetization andcomposition of the free layer 25 are the same as described previously.Above the free layer in the top portion 26 are sequentially formed aspacer, a pinned layer which may have a SyAP configuration, an AFMlayer, and a cap layer. The aforementioned layers have the samecomposition and magnetization direction as in the previously describedbottom portion of the bottom spin valve structure. The layers in the topportion 26 of the top spin valve embodiment are not shown in order tosimplify the drawing and direct attention to the abutting junctionformed between the free layer 25 and the hard bias structure on eitherside of the GMR element.

In the presence of an appropriately sized external magnetic field whichcan be applied when the magnetic head 20 is passed over a magneticrecording medium in the z direction, the magnetization direction in thefree layer 25 switches to the y or −y direction. The changed magneticstate in the free layer 25 may be sensed by passing a current throughthe GMR element to detect a lower resistance than when the magnetizationof the pinned layer and free layer are orthogonal to each other.

Next, a seed layer 28 such as CrTi with a thickness between about 10 and100 Angstroms and preferably about 30 Angstroms is deposited on thefirst gap layer 23 by a sputtering method or ion beam deposition (IBD).Alternatively, the seed layer 28 may be one of TiW, CrMo, or othermaterials that have a body centered cubic (BCC) lattice structure andhave good lattice matching with a subsequently deposited underlayer andhard bias layer.

An important feature of the present invention is the hard bias structure32 which is deposited on the seed layer 28. In one aspect, the hard biasstructure 32 is comprised of a stack of layers including an underlayer29 formed on the seed layer 28 and a composite hard bias layer disposedon the underlayer 29. The composite hard bias layer consists of a lowerhard bias layer 30 hereafter referred to as HB1 and an upper hard biaslayer 31 hereafter referred to as HB2. In the exemplary embodiment, thehard bias structure is formed by a sputtering or IBD method. Optionally,the composite hard bias layer may be formed directly on the seed layer28 by omitting the underlayer 29 although this arrangement is generallyless desirable.

In one embodiment, the underlayer 29 is a FeCoMo layer that has acomposition represented by Fe_(R)CO_(S)MO_(T) wherein R, S, and T arethe atomic % of Fe, Co, and Mo, respectively, and wherein R+S+T=100 andR is from about 10 to 90, S is between about 10 and 90, and T is fromabout 5 to 20. Preferably, the thickness of the underlayer 29 is fromabout 5 to 40 Angstroms but may vary depending upon the desiredthickness of the hard bias structure and the thickness of the overlyingcomposite hard bias layer. The underlayer 29 has a high magnetic momentand a lattice structure intermediate between that of the seed layer 28and the HB1 layer 30 in order to provide good lattice matching.Optionally, the underlayer 29 may be made of a BCC ferromagneticmaterial such as FeCo, FeCoCr, FeCr, FeV, FeTa, FePd, FeHf, FePt, FeW,or the like that has a high magnetic moment represented by the equation4πMs≧10000 and which has good lattice matching with hard bias layerssuch as those based on a CoCrPt alloy.

In one embodiment, the HB1 layer 30 is comprised of a CoCrPt alloy thathas a composition represented by Co_(X)Cr_(Y)Pt_(Z) in which X, Y, and Zare the atomic % of Co, Cr, and Pt, respectively, and wherein X+Y+Z=100and X is from about 50 to 80, Y is between 0 and about 20, and Z is from0 to about 50. Preferably, the HB1 layer 30 has a composition that is78.6 atomic % Co, 5.2 atomic % Cr, and 16.2 atomic % Pt which ishereafter referred to as Co_(78.6)Cr_(5.2)Pt_(16.2). This composition istypically employed in prior art CoCrPt hard bias layers. The Crcomponent serves to improve corrosion resistance and magnetic domainstructure while the Pt component is used to control coercivity. Thethickness of the HB1 layer 30 is from about 10 to 50 Angstroms. Thethickness may be adjusted to optimize the Hc, Mrt, and S values for thehard bias structure 32. It is understood that each of the layers in thehard bias structure 32 has a Hc, Mrt, and S component and that magneticcoupling between the layers produces Hc, Mrt, and S values for the hardbias structure that influences the adjacent free layer 25 and ensures asingle domain state formed therein. Note that the CoCrPt alloy of thepresent invention encompasses a CoPt layer (Y=0) and a CoCr layer (Z=0).

Alternatively, the HB1 layer 30 may be comprised of another materialsuch as FePt that has a high coercivity and good lattice matching with aBCC underlayer 29 and with a BCC seed layer 28. Preferably, the HB1layer has a minimum Hc value of greater than 1000 Oe and has an Mrtvalue in the range of about 0.1 to 0.5.

In the embodiment where the HB1 layer 30 is comprised of aCo_(78.6)Cr_(5.2)Pt_(16.2) layer, the HB2 layer 31 preferably has athickness between about 50 and 300 Angstroms and a compositionrepresented by Co_(X)Cr_(Y)Pt_(Z) in which X, Y, and Z are the atomic %of Co, Cr, and Pt, respectively, and wherein X+Y+Z=100 and X is about65, Y is about 15, and Z is about 20 which is hereafter referred to asCo₆₅Cr₁₅Pt₂₀. The inventors have surprisingly found that a compositehard bias layer with a Co_(78.6)Cr_(5.2)Pt_(16.2)/Co₆₅Cr₁₅Pt₂₀ (HB1/HB2)configuration has a higher coercivity than a single hard bias layerbased on a CO_(78.6)Cr_(5.2)Pt_(16.2) alloy. As shown in Table 1, thethickness of the HB2 layer 31 may also be adjusted to optimize H_(c) andMrt values for the hard bias structure 32. Preferably, the HB2 layer 31thickness is about 2 to 10 times that of the HB1 layer 30 thickness andthe combined thicknesses of the HB1 and HB2 layers is between about 150and 350 Angstroms. At least one of the HB1 and HB2 layers 30, 31 formsan abutting junction with the free layer 25 in the GMR element. A higherCr content in the HB2 layer provides for more grain segregation while ahigher Pt content provides for a higher coercivity and lower moment thanin the HB1 layer.

TABLE 1 Magnetic Properties of Hard Bias Structure on a 30 Angstromthick CrTi Seed Layer FeCoMo Co_(78.6)Cr_(5.2)Pt_(16.2) Co₆₅Cr₁₅Pt₂₀ HcSample (Angstroms) (Angstroms) (Angstroms) Mrt (Oe) S S* S1 — 130 — 11925 0.89 0.93 S2 — 50 150 1 2350 0.9 0.93 S3 15 130 — 1.34 1350 0.880.93 S4 15 50 150 1.33 1573 0.89 0.92 S5 15 40 130 1.16 1511 0.89 0.92S6 20 40 150 1.35 1422 0.89 0.93 S7 20 30 140 1.22 1385 0.89 0.93

In Table 1, samples S1 and S3 are examples of prior art hard biasstructures previously employed by the inventors. Note that while theinsertion of a FeCoMo underlayer in S3 has the desired effect ofincreasing Mrt (mem μ/cm²) compared to that of S1, the Hc value suffersa substantial reduction. One advantage of the present invention is thatwhen no underlayer is present on the seed layer, a composite hard biaslayer such as the one represented by theCo_(78.6)Cr_(5.2)Pt_(16.2)/Co₆₅Cr₁₅Pt₂₀ (HB1/HB2) configuration in S2provides a higher coercivity than a single Co_(78.6)Cr_(5.2)Pt_(16.2)hard bias layer in S1. This advantage also holds for theCO_(78.6)Cr_(5.2)Pt_(16.2)/Co₆₅Cr₁₅Pt₂₀ configuration on a FeCoMounderlayer (S4) compared to a Co_(78.6)Cr_(5.2)Pt_(16.2)/FeCoMo stack inS3. Thus, in a hard bias structure where a BCC underlayer is inserted toincrease Mrt, the composite hard bias layer of the present invention isable to increase the coercivity (Hc) with a minimal effect on Mrt.Furthermore, the inventors have verified that asymmetry sigma is loweredwhen a composite HB1/HB2 hard bias layer of the present invention isincorporated in a hard bias structure with a BCC underlayer.

Samples S5, S6, and S7 show various thicknesses for the HB1 and HB2layers and demonstrate that the Mrt can be fine tuned to provide anoptimum value for Hc which in this case occurs for sample S4. Meanwhile,a high squareness (S) value and a high coercive force angle ratio (S*)are maintained in all samples with the HB1/HB2 composite hard biaslayer. A second advantage as a result of the capability to fine tune theMrt value is that a higher process window may be realized when formingthe hard bias structure. In other words, by simultaneously optimizingMrt and Hc, small variations in the thickness of the layers within thehard bias structure 32 will have a minimal effect on Mrt and Hc.

In an alternative embodiment where the HB1 layer 30 is formed of amaterial other than a CoCrPt alloy, a HB2 layer 31 composition isselected that has a high coercivity, a magnetic moment similar to thatof Co₆₅Cr₁₅Pt₂₀ and which provides good lattice matching with the HB1layer. Furthermore, the HB1 and HB2 layer requirements and relationshipsdescribed earlier are also applicable in this case. The thicknesses ofthe HB1 and HB2 layers 30, 31 may be adjusted to optimize Hc and Mrtvalues for the hard bias structure 32.

The present invention also encompasses a hard bias structure 32 whereinthe HB2 layer 31 is formed directly on the BCC underlayer 29 and has acomposition represented by Co_(X)Cr_(Y)Pt_(Z) in which X, Y, and Z arethe atomic % of Co, Cr, and Pt, respectively, and wherein X+Y+Z=100 andX is about 65, Y is about 15, and Z is about 20. Preferably, the HB2layer 31 is a Co₆₅Cr₁₅Pt₂₀ layer. In other words, the thickness (andmoment contribution) from the HB1 layer 30 can be reduced to zero. Sincea Co₆₅Cr₁₅Pt₂₀ layer has a smaller magnetic moment (˜40% less) than aCo_(78.6)Cr_(5.2)Pt_(16.2) layer, the thickness of the HB2 layer 31 isincreased in order to match the total Mrt of a compositeCo_(78.6)Cr_(5.2)Pt_(16.2)/Co₆₅Cr₁₅Pt₂₀ layer. Optionally, the HB2 layeris made thicker to match the Mrt of a Co_(78.6)Cr_(5.2)Pt_(16.2) layersuch as sample S1 that is used in the prior art. The HB2 layer whenformed on the BCC underlayer 29 may have a thickness in the range ofabout 50 to 300 Angstroms. As a result of the thicker Co₆₅Cr₁₅Pt₂₀ layeralong the junction edge with the free layer 25, the junction coveragewill be more uniform and the coercivity of the HB2 layer 31 along thetapered junction edge will be larger. Furthermore, a Co₆₅Cr₁₅Pt₂₀ layerhas smaller anisotropy energy than a Co_(78.6)Cr_(5.2)Pt_(16.2) layerand therefore tends to have less easy axis dispersions when it isexchanged coupled with a magnetic underlayer such as FeCoMo. Theinventors have surprisingly found improved performance when aCo₆₅Cr₁₅Pt₂₀/FeCoMo hard bias structure is substituted for theCo_(78.6)Cr_(5.2)Pt_(16.2)/FeCoMo configuration in sample S3 (Table 1).

The properties of the hard bias structure of the present invention arevery stable with or without annealing. Although no annealing isnecessary, the hard bias structure 32 may be annealed by heating thesubstrate 21 at a temperature of about 200° C. to 250° C. in a N₂ambient for a period of about 0.5 to 5 hours.

An electrical lead 33 is deposited by a sputtering or IBD method on theHB2 layer 31 on each side of the GMR element. Although the leads 33 areconnected to the sides of the GMR element on the top portion 26 in theexemplary embodiment, the present invention also anticipates aconfiguration in which the leads are attached to the top surface 26 a(FIG. 4) of the top portion. The leads may be a composite layer in whicha thicker conductive layer such as Au or Cu is sandwiched betweenthinner Ta layers. In one embodiment (not shown), the leads 29 arecomprised of a 30 Angstrom thick first Ta layer on the HB2 layer 31, a400 Angstrom thick gold or copper layer on the first Ta layer, and a 30Angstrom thick second Ta layer on the gold or copper layer. The bottomTa layer serves as an interrupt layer to provide a good crystallographicmatch between the HB2 layer 31 and the gold or copper lead layer.

Referring to FIG. 4, a conventional lift-off process is used to removethe photoresist layer 27 and the overlying seed layer 28, underlayer 29,HB1 and HB2 layers 30, 31 and the lead layer 33. A track width TW isdefined as the distance between the leads 33 on the top surface 26 a ofthe GMR element. A second gap layer 34 is disposed on the leads 33 andtop portion 26 and a second shield layer 35 is formed on the second gaplayer 34 to complete the magnetic read head 20. Note that the secondshield layer 35 preferably has a smooth top surface in order to improvethe process latitude for subsequent process steps that could involve awrite head fabrication as an example.

A second embodiment will now be described in which a hard bias structureformed adjacent to a free layer in a magnetoresistive (MR) element iscomprised of laminated hard bias layers. In the exemplary embodimentpictured in FIGS. 5-6, the hard bias structure is formed in a magneticread head and adjacent to a GMR element that was described previously inthe first embodiment. However, the second embodiment also encompassesany configuration where a hard bias structure described herein forms anabutting junction with a free layer in a MR element.

Referring to FIG. 5, a first shield layer 22 and a first gap layer 23are provided on a substrate 21 as previously described. Likewise, a GMRelement comprised of a bottom portion 24, a free layer 25, and a topportion 26 is then fabricated on the first gap layer according to amethod described in the first embodiment in which a patternedphotoresist layer 27 having a width w serves as an etch mask. A seedlayer 28 comprised of CrTi with a thickness of about 30 Angstroms isdeposited on the exposed regions of the first gap layer 23 by asputtering or IBD process. Alternatively, the seed layer 28 may be oneof TiW, CrMo, or another material that has a body centered cubic (BCC)lattice structure and good lattice matching with a subsequentlydeposited underlayer and hard bias layer.

An important feature of the present invention is the hard bias structure40 which is deposited on the seed layer 28. In one aspect, the hard biasstructure 40 is made of laminated layers in which a stack comprised ofan underlayer 29 and a composite hard bias layer on the underlayer isrepeated two or more times to form a plurality of stacks. For example, abottom layer in a second stack is formed on the top layer of a firststack and so forth. Optionally, the underlayer 29 may be omitted fromone or more stacks in the hard bias structure although this arrangementis generally less desirable. In the exemplary embodiment, a second stackof three layers is formed on a first stack of three layers. However,more than two stacks of layers may be formed as appreciated by thoseskilled in the art. The laminated hard bias structure 40 is fabricatedby a conventional means which may involve magnetron sputtering, forexample.

The first stack of three layers in the hard bias structure 40 consistsof an underlayer 29 a, a lower hard bias (HB1) layer 30 a, and an upperhard bias (HB2) layer 31 a. In one aspect, the underlayer 29 a is aFeCoMo layer that has a composition represented by Fe_(R)Co_(S)Mo_(T)wherein R, S, and T are the atomic % of Fe, Co, and Mo, respectively,and wherein R+S+T=100 and R is from about 10 to 90, S is between about10 and 90, and T is from about 5 to 20. Preferably, the thickness of theunderlayer 29 a is from about 5 to 40 Angstroms but may vary dependingupon the desired thickness of the hard bias structure, the number ofstacks employed, and the thickness of the overlying composite hard biaslayer. The underlayer 29 a has a high magnetic moment and a latticestructure intermediate between that of the seed layer 28 and the HB1layer 30 a in order to provide good lattice matching. Optionally, theunderlayer 29 a may be made of a BCC ferromagnetic material such asFeCo, FeCoCr, FeCr, FeV, FeTa, FePd, FeHf, FePt, FeW, or the like thathas a high magnetic moment represented by the equation 4πMs≧10000 andwhich has good lattice matching with hard bias layers such as thosebased on a CoCrPt alloy.

In one embodiment, the HB1 layer 30 a is comprised of a CoCrPt alloythat has a composition represented by Co_(X)Cr_(Y)Pt_(Z) in which X, Y,and Z are the atomic % of Co, Cr, and Pt, respectively, and whereinX+Y+Z=100 and X is from about 50 to 80, Y is between 0 and about 20, andZ is from 0 to about 50. Preferably, the HB1 layer 30 a is aCo_(78.6)Cr_(5.2)Pt_(16.2) layer. The thickness of the HB1 layer 30 a isfrom about 10 to 50 Angstroms but may vary depending on the number ofstacks in the laminated hard bias structure and may be adjusted tooptimize the Hc, Mrt, and S values for the hard bias structure 40. It isunderstood that each of the layers in the hard bias structure 40 has aHc, Mrt, and S component and that magnetic coupling between the layersproduces Hc, Mrt, and S values for the hard bias structure thatinfluences the adjacent free layer 25 and ensures a single domain stateformed therein.

Alternatively, the HB1 layer 30 a may be comprised of another materialsuch as FePt that has a high coercivity and good lattice matching with aBCC underlayer 29 a and with a BCC seed layer 28. Preferably, the HB1layer has a minimum Hc value of greater than 1000 Oe and has an Mrtvalue in the range of about 0.1 to 0.5.

In the embodiment where the HB1 layer 30 a is comprised of aCo_(78.6)Cr_(5.2)Pt_(16.2) layer, the HB2 layer 31 a preferably has athickness between about 50 and 300 Angstroms and is a Co₆₅Cr₁₅Pt₂₀layer. The inventors have unexpectedly found that a composite hard biaslayer with a Co_(78.6)Cr_(5.2)Pt_(16.2)/Co₆₅Cr₁₅Pt₂₀ (HB1/HB2)configuration has a higher coercivity than a single hard bias layerbased on a Co_(78.6)Cr_(5.2)Pt_(16.2) alloy. The thickness of the HB2layer 31 a may also be adjusted to optimize H_(c) and Mrt values in thehard bias structure 40. Preferably, the HB2 layer 31 a thickness isabout 2 to 10 times that of the HB1 layer 30 a thickness and thecombined thicknesses of the HB1 and HB2 layers in the first stack isbetween about 150 and 350 Angstroms.

In an alternative embodiment where the HB1 layer 30 a is formed of amaterial other than a CoCrPt alloy, a HB2 layer 31 a composition isselected that has a high coercivity, a magnetic moment similar to thatof Co₆₅Cr₁₅Pt₂₀ and which provides good lattice matching with the HB1layer and with a subsequently formed underlayer 29 b in the secondstack.

A second stack of layers is formed on the HB2 layer 31 a and iscomprised of from bottom to top in order, a second underlayer 29 b, asecond HB1 layer 30 b, and a second HB2 layer 31 b. The composition andfilm thickness of the second underlayer 29 b is preferably the same asthat described for the underlayer 29 a. Similarly, the composition andthickness of the second HB1 layer 30 b and the second HB2 layer 31 b arepreferably the same as the composition and thickness of the hard biaslayers 30 a, 31 a respectively. However, the thickness and compositionof each of the layers in the first and second stack may be adjusted toprovide optimum Hc and Mrt values for the hard bias structure 40. Notethat at least one of the layers in the hard bias structure forms anabutting junction with an adjacent free layer.

The present invention also encompasses a laminated hard bias structure40 wherein the HB2 layers 31 a, 31 b are preferably Co₆₅Cr₁₅Pt₂₀ layersand are formed directly on the BCC underlayers 29 a, 29 b, respectively.In other words, the thickness (and moment contribution) from the HB1layers 30 a, 30 b can be reduced to zero and the second underlayer 29 bis formed on first HB2 layer 31 a. Since a Co₆₅Cr₁₅Pt₂₀ layer has asmaller magnetic moment (˜40% less) than a Co_(78.6)Cr_(5.2)Pt_(1.62)layer, the thicknesses of the HB2 layers 31 a, 31 b are increasedaccordingly in order to match the total Mrt of aCo_(78.6)Cr_(5.2)Pt_(16.2) layer or a compositeCo_(78.6)Cr_(5.2)Pt_(16.2)/Co₆₅Cr₁₅Pt₂₀ layer as referred to in Table 1.At least one of the HB2 layers 31 a, 31 b adjoins each side of the freelayer 25. The advantages of a hard bias structure comprised of a BCCunderlayer/Co₆₅Cr₁₅Pt₂₀ configuration are similar to those mentioned inthe first embodiment.

Although no annealing is necessary to stabilize the properties of thelayers within the hard bias structure 40, the hard bias structure may beannealed by heating the substrate 21 at a temperature of about 200° C.to 250° C. in a N₂ ambient for a period of about 0.5 to 5 hours.

Electrical leads 33 are formed on the hard bias structure 40 by aconventional process. In one embodiment, the leads 33 are comprised of acomposite TalAu/Ta layer in which a 30 Angstrom thick first Ta layer issputter deposited on the hard bias structure 40, a 400 Angstrom thick Aulayer is sputter deposited on the first Ta layer, and a 30 Angstromthick second Ta layer is sputter deposited on the Au layer. Optionally,Cu may be used in place of Au in the lead layer. Although the leads 33are shown connected to the sides of the top portion 26 of the GMRelement, the invention also anticipates a configuration in which theleads are attached to the top surface 26 a of the top portion 26.

Referring to FIG. 6, the photoresist layer 27 and overlying seed layer28, hard bias structure 40, and lead 33 are removed by a well known liftoff process to leave the top surface of the top portion 26 exposedbetween the leads 33. A second gap layer 34 is deposited on the leads 33and top portion 26 as described previously. Subsequently, a secondshield layer 35 is formed on the second gap layer 34 according to theprocess included in the first embodiment.

The advantages of the second embodiment are the same as described in thefirst embodiment. First, the hard bias structure of the presentinvention provides a higher coercivity than a single hard bias layerbased on Co_(78.6)Cr_(5.2)Pt_(16.2) or CoPt in the prior art. Moreover,in a hard bias structure where a BCC underlayer is inserted to increaseMrt, the hard bias structure of the present invention is able toincrease the coercivity (Hc) with a minimal effect on Mrt. In otherwords, the loss in Hc due to insertion of an underlayer in the hard biasstructure of the present invention is compensated by the higher initialHc value generated by the composite hard bias layer or by a thickerCo₆₅Cr₁₅Pt₂₀ layer. As a result, the output asymmetry is reduced duringa read operation.

Another advantage is the capability to fine tune the Mrt value so that ahigher process window may be realized when forming the hard biasstructure. Therefore, small variations in the thickness of the variouslayers within the hard bias structure will have a minimal effect on themagnitude of the Hc and Mrt values.

While this invention has been particularly shown and described withreference to, the preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of this invention.

1. A hard bias structure for providing a longitudinal bias to a freelayer in a spin valve within a magnetic read head, comprising: (a) afirst hard bias layer formed on a substrate and on either side of a spinvalve, said first hard bias layer has a first thickness, a coercivityHc, a top surface, and an Mrt value; and (b) a second hard bias layerformed on the top surface of the first hard bias layer, said second hardbias layer has a second thickness greater than said first thickness, anMrt value, and a coercivity greater than that of the first hard biaslayer, wherein at least one of the first and second hard bias layerscontacts said free layer in the spin valve and said first and secondhard bias layers form a first composite hard bias layer.
 2. The hardbias structure of claim 1 wherein said first hard bias layer iscomprised of a Co_(78.6)Cr_(5.2)Pt_(16.2) layer.
 3. The hard biasstructure of claim 1 wherein said second hard bias layer is comprised ofa Co₆₅Cr₁₅Pt₂₀ layer.
 4. The hard bias structure of claim 1 wherein saidsecond thickness is about 2 to 10 times greater than said firstthickness and wherein the first thickness and second thickness form atotal hard bias structure thickness of about 150 to 350 Angstroms.
 5. Ahard bias structure for providing a longitudinal bias to a free layer ina spin valve within a magnetic read head, comprising: (a) a firstunderlayer that has a body centered cubic (BCC) lattice structure and isformed on a substrate and on either side of said spin valve; (b) a firsthard bias layer formed on said first underlayer, said first hard biaslayer has a first thickness, a coercivity Hc, a top surface, and an Mrtvalue; and (c) a second hard bias layer formed on the top surface of thefirst hard bias layer, said second hard bias layer has a secondthickness greater than said first thickness, an Mrt value, and acoercivity greater than that of the first hard bias layer, wherein atleast one of the first and second hard bias layers contacts said freelayer and said first and second hard bias layers form a first compositehard bias layer.
 6. The hard bias structure of claim 5 wherein saidfirst underlayer is comprised of FeCoMo and has a thickness betweenabout 5 and 40 Angstroms.
 7. The hard bias structure of claim 5 whereinsaid first underlayer is one of FeCo, FeCoOr, FeCr, FeV, FeTa, FePd,FeHf, FePt, or FeW.
 8. The hard bias structure of claim 5 wherein saidfirst hard bias layer has a composition represented byCo_(X)Cr_(Y)Pt_(Z) in which X, Y, and Z are the atomic % of Co, Cr, andPt, respectively, and wherein X+Y+Z=100 and X is from about 50 to 80, Yis between 0 and about 20, and Z is from 0 to about
 50. 9. The hard biasstructure of claim 5 wherein said first hard bias layer is comprised ofa Co_(78.6)Cr_(5.2)Pt_(16.2) layer.
 10. The hard bias structure of claim5 wherein said second hard bias layer has a composition represented byCo_(X)Cr_(Y)Pt_(Z) in which X, Y, and Z are the atomic % of Co, Cr, andPt, respectively, and wherein X+Y+Z=100 and X is about 65, Y is about15, and Z is about
 20. 11. The hard bias structure of claim 5 whereinsaid second thickness is about 2 to 10 times greater than said firstthickness and wherein the first thickness and second thickness form afirst composite hard bias layer thickness of about 150 to 350 Angstroms.12. The hard bias structure of claim 5 wherein said substrate has a toplayer which is a seed layer comprised of CrTi.
 13. A magnetic read headbased on a magnetoresistive (MR) element, comprising: (a) a substrateupon which a MR element has been formed, said MR element has a topsurface and two sides and is comprised of a free layer that has twosidewalls coincident with said two sides; (b) a seed layer formed onsaid substrate and adjacent to each side of said MR element; (c) anunderlayer that has a BCC lattice structure disposed on said seed layer;(d) a first hard bias layer formed on said underlayer, said first hardbias layer has a first thickness, a coercivity (Hc), a top surface, andan Mrt value; (e) a second hard bias layer formed on the top surface ofthe first hard bias layer, said second hard bias layer has a secondthickness greater than said first thickness, an Mrt value, and acoercivity greater than that of the first hard bias layer; and (f) anelectrical lead layer formed above each second hard bias layer thatcontacts said MR element on each of its two sides such that a spacebetween the electrical leads and above the top surface of said MRelement defines the track width of said magnetic read head, wherein atleast one of the first and second hard bias layers contacts eachsidewall of said free layer in the MR element and said first and secondhard bias layers form a first composite hard bias layer.
 14. Themagnetic read head of claim 13 wherein said underlayer and firstcomposite hard bias layer form a hard bias structure that provideslongitudinal biasing to said free layer.
 15. The magnetic read head ofclaim 13 wherein said seed layer has a BCC lattice structure and athickness between about 10 and 100 Angstroms.
 16. The magnetic read headof claim 13 wherein said seed layer is one of CrTi, TiW, or CrMo. 17.The magnetic read head of claim 13 wherein said underlayer is a magneticlayer which has a BCC lattice structure and a thickness between about 5and 40 Angstroms.
 18. The magnetic read head of claim 13 wherein saidunderlayer is one of FeCoMo, FeCo, FeCoCr, FeCr, FeV, FeTa, FePd, FeHf,FePt, or FeW.
 19. The magnetic read head of claim 13 wherein said firsthard bias layer has a composition represented by Co_(X)Cr_(Y)Pt_(Z) inwhich X, Y, and Z are the atomic % of Co, Cr, and Pt, respectively, andwherein X+Y+Z=100 and X is from about 50 to 80, Y is between 0 and about20, and Z is from 0 to about
 50. 20. The magnetic read head of claim 13wherein said first hard bias layer comprised ofCo_(78.6)Cr_(5.2)Pt_(16.2), CoPt, CoCr, or FePt.
 21. The magnetic readhead of claim 13 wherein said second hard bias layer has a compositionrepresented by Co_(X)Cr_(Y)Pt_(Z) in which X, Y, and Z are the atomic %of Co, Cr, and Pt, respectively, and wherein X+Y+Z=100 and X is about65, Y is about 15, and Z is about
 20. 22. The magnetic read head ofclaim 13 wherein said second thickness is about 2 to 10 times greaterthan said first thickness and wherein the first thickness and secondthickness form a first composite hard bias layer thickness of about 150to 350 Angstroms.
 23. A method of forming a hard bias structure in amagnetic read head based on an MR element, comprising: (a) providing asubstrate on which an MR element having a top surface and two sides andthat is comprised of a free layer which has two sidewalls coincidentwith said sides is formed; (b) forming a seed layer on said substrateand adjacent to each side of said MR element; (c) depositing a first BCCunderlayer on said seed layer; and (d) depositing a first composite hardbias layer on said first BCC underlayer; said first composite hard biaslayer is comprised of a lower first hard bias layer that has a firstthickness and a top surface, and an upper second hard bias layer formedon the top surface of the lower first hard bias layer and having asecond thickness greater than the first thickness and wherein at leastone of said first and second hard bias layers contacts each sidewall ofsaid free layer.
 24. The method of claim 23 further comprised of formingan electrical lead on the first composite hard bias layer on each sideof the MR element wherein each electrical lead contacts said MR elementand a space between said electrical leads defines the track width ofsaid magnetic read head.
 25. The method of claim 23 wherein saidunderlayer and first composite hard bias layer form a hard biasstructure that has a coercivity (Hc) and an Mrt value which provides alongitudinal bias to ensure a single magnetic domain in said free layer.26. The method of claim 23 wherein the BCC underlayer has an Ms valuethat satisfies the equation 4πMs≧10000.
 27. The method of claim 23wherein said substrate is a first shield layer in said magnetic readhead.
 28. The method of claim 23 wherein said seed layer is comprised ofTiCr, TiW, or MoCr and has a thickness of about 10 to 100 Angstroms. 29.The method of claim 23 wherein said BCC underlayer is a magnetic layerthat has a BCC lattice structure and a thickness between about 5 and 40Angstroms.
 30. The method of claim 23 wherein said BCC underlayer is oneof FeCoMo, FeCo, FeCoCr, FeCr, FeV, FeTa, FePd, FeHf, FePt, or FeW. 31.The method of claim 23 wherein said first hard bias layer has acomposition represented by Co_(X)Cr_(Y)Pt_(Z) in which X, Y, and Z arethe atomic % of Co, Cr, and Pt, respectively, and wherein X+Y+Z=100 andX is from about 50 to 80, Y is between 0 and about 20, and Z is from 0to about
 50. 32. The method of claim 23 wherein said first hard biaslayer is a Co_(78.6)Cr_(5.2)Pt_(16.2) layer.
 33. The method of claim 23wherein said second hard bias layer has a composition represented byCo_(X)Cr_(Y)Pt_(Z) in which X, Y, and Z are the atomic % of Co, Cr, andPt, respectively, and wherein X+Y+Z=100 and X is about 65, Y is about15, and Z is about
 20. 34. The method of claim 23 wherein said secondthickness is about 2 to 10 times greater than said first thickness. 35.The method of claim 23 wherein said first composite hard bias layer hasa thickness of about 150 to 350 Angstroms.